Primary immune deficiency diseases (PID) provide an excellent window into the functioning of the immune system. During the past 15 years the molecular basis of more than 100 PID has been elucidated. The purpose of the bi-annual meeting of the International Union of Immunological Societies (IUIS) Expert Committee on PID is to update the community of scientists and physicians who work in PID to advances in the field of basic and clinical science that have impact on the investigation, diagnosis and care of patients with PID. The meeting also serves to stimulate clinical trials in the field of PIDs, including the development of novel therapeutic strategies. The meeting is structured over 3 days. The first 2.5 days consist of approximately 5 scientific sessions, in which basic science presentations of cutting edge research in immunology are followed by presentations describing novel gene defects or new understandings of the structure and function of previously described genes deficient in patients with PID or new therapies for PID. There are normally a total of about 30 speakers. The Faculty includes distinguished scientists who have significantly contributed to advances in molecular and cellular immunology, biochemistry, and cell signaling and of translational researchers who have made advances in the pathophysiology diagnosis and treatment of PID during the past two years. The meeting is attended by approximately 100-120 invited physicians and scientists who are actively engaged in PID research and patient care all over the world.The scientific sessions are followed by a half day meeting of the Committee of Experts on PID to update the classification of PID. During this meeting the classification tables of PID from the previous meeting are updated the published in ahigh impact immunology journal. We are seeking support for three meetings to be held in 2005, 2007 and 2009. The 2005 meeting will be held June 17-19 in Budapest, Hungary.